Host-associated differentiation in a pecan and water hickory Aphidomorpha community

Authors: MEDINA, R. - Texas A&M University; Dickey, Aaron; HARRISON, K. - Texas A&M University; Miller, Gary

Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2016
Publication Date: 3/14/2017
Citation: Medina, R.F., Dickey, A.M., Harrison, K., Miller, G.L. 2017. Host-associated differentiation in a pecan and water hickory Aphidomorpha community. Entomologia Experimentalis et Applicata. 162:366-378.

Interpretive Summary: Aphids and phylloxerans are pests that feed on many of the world’s agriculturally important crops, trees, and ornamental plants. They are also one of the most important insects in the role of transmission of plant diseases and contribute to billions of dollars in agricultural losses worldwide. Aphids and phylloxerans also damage plants through their direct feeding. Proper identification is paramount before any scientific study can be performed. This research concentrates on the ecology of six species of aphids and phylloxerans and their host plants: pecan and water hickory trees. Genetic markers were developed in order to detect the presence of genetically distinct, host-associated populations for each insect species and the ecology of six aphids and phylloxerans was studied to determine if the formation of genetically distinct, host-associated populations is created and maintained by ecological reproductive isolation. This information will be useful to biologists and ecologists, insect taxonomists and systematists.

Technical Abstract: Host-Associated Differentiation (HAD) is the formation of genetically distinct, host-associated populations created and maintained by ecologically-mediated reproductive isolation. HAD potentially accounts for a high level of species diversity in parasites, including herbivorous insects. While case studies testing the occurrence of HAD are accumulating, it is still unclear how common HAD is and which specific ecological traits explain its occurrence. To address these issues, studies are needed that include negative results (i.e., instances in which parasite populations do not exhibit HAD) and test for HAD across communities (i.e., several parasite species on the same set of host species). In this study, HAD was tested in a community of six species of Aphidomorpha that share a host-plant pair: pecan and water hickory trees. All six species are parthenogenetic and three species are endophagous, traits putatively involved in the generation and maintenance of HAD. AFLP markers were developed in order to detect the presence of genetically distinct, host-associated populations for each insect species. Strict HAD (i.e., the occurrence of genetically distinct pecan- and a water hickory-associated genotypes) was found in Phylloxera notabilis, P. devastatrix, and Monelliopsis pecanis. Monellia caryella showed a pattern of partial HAD (i.e., the occurrence of a genetically distinct water hickory-associated genotype but not a pecan-associated genotype). No HAD was found in Melanocallis caryaefoliae or P. texana. By comparing the pattern of HAD presence in the pecan/water hickory Aphidomorpha community, it is concluded that neither parthenogenesis nor endophagy sufficiently explain the occurrence of HAD in this system.